Implants such as implantable heart pacemakers, ICDs or monitoring devices, which record intracardiac electrocardiograms and obtain marker signals, are essentially known. Intracardiac electrocardiograms (IEGM) are typically in the form of a chronological series of values representing a time-scanned, originally analog signal. Such an electrocardiogram has various typical and periodically recurring signal features representing cardiac events such as contractions of the right or left ventricle, or contractions of the right or left atrium. Signal features representing contractions of the right or left atrium are typically denoted as P waves, while signal features associated with contraction of the ventricle are reflected in a so-called R wave. On the basis of such an electrocardiogram, the implant generates marker signals, which mark the chronological occurrence of detected cardiac events by the fact that the implant detects P waves and R waves, e.g., through a suitable comparison of threshold values. To do so, an intraatrial cardiogram is typically sent to an atrial sensing unit of the implant; the intraatrial electrocardiogram signals thereby picked up are constantly compared to a threshold value; and a marker signal reflecting an atrial event, i.e., contraction of the atrium, is generated when the threshold value is exceeded. Similarly, an intraventricular electrocardiogram is regularly compared with a threshold value by a ventricular sensing unit, and when this threshold value is exceeded, a ventricular marker signal is generated, marking the contraction of the corresponding ventricle. Other typical marker signals contain information about the evaluation and reaction (e.g., treatment) of the implant.
The background is that the contraction of an atrium or a ventricle is associated with depolarization of the respective myocardium (heart muscle tissue), leading to detectable potentials that can be picked up by intraatrial or intraventricular electrodes and ultimately lead to the corresponding signals in the intraatrial and intraventricular electrogram.
Via a corresponding interface for wireless data transmission, such implants are capable of transmitting recorded electrograms by telemetry in the form of electrocardiogram signals as well as marker signals derived from the electrocardiograms to an external device.